Synchronizing system



0a.- 22, 1929. P. moms v ,732,734

I SYNCHRONIZING- SYSTBI Filed Oct 20, 1927 4 ShoetwSheet 2 Fly. 5. Fly. 6.

o 0- 25/ o 100% Line Volta -A Phase Angle B INVENTOR Phillips Thomas A'TToRNEY Patented Oct. 22, 1929 UNITED STATES PATENT OFFICE PHILLIPS THOMAS, OF EDGEWOOD, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA SYN CHRONIZIN G SYSTEM Application filo-d October 20, 1927. Serial No. 227,461.

This invention pertains to synchronizing relay systems in which upon the occurrence of certain conditions in a plurality of alternating current circuits, a connecting switch will be closed to parallel the circuits.

The main object of my invention is to provide a relay system for automatically controlling the paralleling of alternating-current circuits.

A secondary object is to produce a device of the character described which shall be inexpensive in construction and reliable and positive in operation.

A further object of my invention is to provide means whereby the closing of the paralleling switch is initiated ata time pre- ,vious to the occurrence of exact phase coincidence so that the paralleling switch, which requires a definite time for its operation, will be finally closed precisely at the moment of exact coincidence.

Another object of my invention is to control the energization of the paralleling relay by means of the resultant of the voltages of the circuits to be paralleled.

A further object is to make provision for compensation for a decrease in the voltage of one of the circuits so that paralleling will be accomplished more quickly if the voltage of one of the circuits is below normal.

A still further object of my invention is to cause the alternating-current circuits to be paralleled iftheir voltages are at a predetermined phase angle and approaching coincidence at a predetermined rate, and to positively prevent paralleling when these voltages are exactly in phase but are departing from the zero phase angle condition when a predetermined circuit has a frequency higher than that of the other.

A still further object is to cause paralleling to take place when the voltages of the circuits are approaching coincidence at a predetermined rate and to prevent paralleling when the voltages are exactly in phase but departing from that condition, regardless of which circuit has the higher frequency.

A further object is to design a relay system which shall perform all of the functions above enumerated.

ures are indicated by the same numerals and in which:

Figure 1 is a diagram of the circuit employed to obtain closing of the paralleling switch precisely at synchronism;

Figs. 2 and 3 are vector diagrams showing the relations of the voltages of the circuits;

Fig. 4 is a diagram of a circuit in which the resultant of the voltages of the circuits to be paralleled is utilized to control the operation of the paralleling switch;

Fig. 5 is a diagram similar to that of Fig. 4,-but so modified that compensation is provided for variations in the voltage of one circuit;

Figs. 6 and 7 are diagrams showing, graphically, the operation of. the voltage compensator Fig. 8 is a diagram of a circuit similar to that of Fig. 5, with the exception that a transformer connected to one of the circuits and to a rectifier is substituted for the battery of Fig. 5, as a source of direct-current potential;

Fig. 9 is a diagram of the circuit utilized to obtain closing of the paralleling switch exactly at synchronism and to prevent paralleling it the voltages are departing from synchronism, if a predetermined circuit has the higher frequency;

Fig. 10 is a vector diagram showing the relation of the voltages in the circuits of Fig. 9;

Fig. 11 is a diagram of the circuit employed to obtain advance initiation of the paralleling switch, regardless of which circuit has the higher frequency; and

Fig. 12 is a vector diagram showing the relation of the voltages in the circuit of Fig. 11.

In Fig. 1, are shown two alternating-ourrent circuits, 12, which may be a distribution system, and 34, which may be connected to a generator. A switch .5' is provided to connect the circuits in parallel. The switch 5 is operated by a solenoid 6. Transformers 7 and 8 are connected, through switches 9 and 10, to the circuits 12 and 3-4, respectively. Between transformer 8 and the circuit 3-4 is inserted a phase splitter consisting of resistor 16 and a reactor 17, the purpose of which will hereinafter appear.

In series with the secondaries of transformers 7 and 8 is connected the thermal element of a thermal relay 11, As a specific example of the thermal relay, I have illustrated a thermionic discharge device, but I wish it to be understood that any thermal relay having similar characteristics may be substituted.

The plate circuit of the relay 11 includes a battery '12 and the operating coil of a relay 13 which, when energized, closes it switch 14. Switch 14 controls a circuit including battery 15 and closing coil 6 of the paralleling switch 5.

In automatic synchronizers of the prior art, the paralleling switch is operated, as a general rule, in response to the operation of a relay having a time delay, which, in turn, is responsive to exact coincidence of the volta es of the circuits to be paralleled. The use o a relay having a certain time delay in its operation is necessary to prevent paralleling on the occurrence of momentary coincidence. Paralleling, therefore, is permitted only when the frequencies of the circuits to be connected are so nearly equal as to make paralleling feasible. In the paralleling system of my invention, this function is performed by the thermal relay which has an inherent delay in its operation because of the time required for heating the thermally-responsive element to its operative temperature, as explained in my co-pending application, Serial No. 215,377 filed August 25, 1927 (W. E. Case 13,459). Because of the size of the paralleling switches now in use on large distribution systems, a considerable period of time is required for their actual operation.

The delay introduced by the paralleling relay of present-systems, added to that required for operation of the paralleling switch, makes it impossible for known synchronizers to connect the circuits to be paralleled precisely at the moment of exact phase coincidence.

This may be observed from a consideration of Fig. 2 in which OL and OM represent line and machine voltages, respectively, and OL and OM the fractions of said line and ma- 'age OM and similarly voltage OL into coincidence with voltage OM, thereby energizing a relay for causing the circuits to be paralleled. If, as is inevitable, a time interval is required for the operation of the paralleling relay and the paralleling switch, it is obvious that, by the time the paralleling switch has finally closed, the voltage OL will have overrun, that is, will have passed through the zero phase-angle condition and will be at an angle in advance of voltage OM, depending upon the sensitiveness of the paralleling relay and the time required for the operation of the paralleling switch.

To avoid paralleling when the voltages of the circuits have passed through zero' phase and are departing therefrom, I make use of the phase splitter of Fig. 1 bywhich I impress upon a relay responsive to coincidence of applied voltages, a voltage in advance of that of one of the circuits by an angle dependent upon the time required for the operation of the paralleling switch 5.

Reference toFig. 3 will explain the operation of my relay system, as shown in Fig. 1. In Fig. 3, OL and OM re resent the line and machine voltages as be ore. OL represents the voltage across the secondary of transformer 7, and OM represents the voltage across secondary of transformer 8. Because of the phase splitter, the voltage across transformer 8 is in advance of that of the machine by an angle which may be adjusted by varying the value of the reactor 17. Assuming clockwise rotation of the vectors in Fig. 3, it will be apparent that, if t e machine is above synchronous speed an slowing down, vectors OM and OM will overtake vector OL. Upon the coincidence of voltages OM and OL, the relay 11 will be energized sufficiently by the cumulative heating effect of both, so that plate current will be initiated and the operating coil of relay-13 energized, as explained in my 00- pending application, Serial No. 215,377. This results in the closing of switch 14 and the energization of the closing coil 6 of the paralleling switch 5. The angular advance of voltage OM ahead of voltage OM may be. so adjusted that the final closing of the paralleling switch will take place just as voltages OM and OL coincide. If it is desired that paralleling occur as the machine is.

brought up to synchronous speed, it is only necessary to substitute an inductance for condenser 17 Obviously, I may use a phase splitter in the line circuit instead of in the machine circuit, in which case, it will merely be necessary to change the sign of the reactance 17, to obtain operation similar to that which occurs when the phase splitter is in the machine circuit.

In Fig. 4 is shown another method of paralleling two alternating-current circuits, but this method does not make use of the phase-advance feature described in connec tion withFig. 1. The resultant of the voltages of circuits 1-2 and 34 is impressed upon the primary of a transformer 18, conductors 1 and 3 being connected conductor 1. The output of transformer 18 is rectified by a rectifier 19 which may be of any type desired but which I have shown as a rectifier of the copper-oxide-disc type. The rectifier output energizes a winding 21 on the center leg of a three-leg transformer which is also provided with a primary winding 22 connected through an impedance 23 to the circuit 3-4. A secondary winding I 24 on the transformer 20 is connected to the filament of a thermal relay 25.' The plate.

- circuitof the relay 25 includes a battery 25' and the coil of a magnetically-operated switch 26 which may be the paralleling switch or a relay controlling the operation of the paralleling switch by means of its contacts 27. -'lhe windings 22 and 24 are equally distributed on the outer legs of the trans former so that the net alternating flux. in

er words, of increasing the magnetizing current which causes the alternating flux. This principle is utilized in my system, as shown inFig. 4, to control the energization of relay 25 which, in turn, controls paralleling of the line and machine circuits. The operation of the system shown in Fig. 4 is as fol lows Assuming that the machine is being brought up to synchronous speed, as long as the line and machine voltages are out of phase, the resultant of these voltages will be effective to energize the primary of transformer 18. The rectifier 19 will, therefore,

have impressed upon it a voltage propor-' tional to the resultant of the line and machine voltages and'will, in turn, supply the winding 21 with direct current in the same proportion. As long as current of a predetermined value circulates through the -winding 21, the reactance of the winding 22 will be low and the current theretbrough comparatively high, and consequently, the voltage drop in the resistor 23 will also be high. when the 'machine has been properly synchronized with theline, the resultant of line and machine voltages decreases to zero, assuming that line and machine voltages are equal. When this condition exists, no current flows through the directcurrent winding of the transformer 20, the reactance of the winding 22 is increased, the current through the winding 22 and the resistor 23' is decreased, the in-phase voltage drop across the resistor 23' is decreased'and the reactive voltage across the primary 22 of transformer 20 is therefore increased. This, of course, results in an increase in. the

voltage across the secondary 24, which causes the filament of the relay 25 to be heated sufficiently to set up a plate current, which will energize the operating coil of switch 26, causing engagement of contacts 27 to parallel the two circuits. Paralleling will not take place, obviously, as long as the resultant of the circuit voltages is sufficient to send an appreciable current through the direct-current winding of the transformer 20 to cause the secondary voltage of the transformer tobe reduced below a point at which the filament of relay 25 is heated sufliciently to set up plate current. The thermal lag of the filament prevents paralleling until the frequencies of the circuits are substantially equal, as explained in my copending application, Serial No. 215,37 7, referred to above.

In paralleling circuits by means of the system shown in Fig. 4, it is desirable, if the line voltage decreases, that paralleling take place more promptly, even though at a considerable phase difference between the voltages and, if the line voltage should decrease markedly, it is then desirable for paralleling to take place regardless of the, phase relation of the voltages. This may be accomplished by the arrangement shown in Fig. 5 which is similar to the system of Fig. 4 ekcept that I have added thereto means for compensating for a decrease in the line voltage whereby, when the line voltage decreases, less exact agreement in phase will be required of the voltages of the circuits for paralleling than when the voltages are both normal.

- Fig. 5 is similar to Fig. 4 except that in Fig. 5, I show a transformer 28 connected to the line 12. A rectifier 31 is connected across the secondary of transformer 28. The output terminals of rectifier 31 are connected in series with those of rectifier 19 and with the coil 21. Opposed to the direct-current voltages of rectifiers 31 and 19 is the voltage of a battery E. Transformer 18, as in Fig.

4 is subject to the resultant of the line and machine voltages.

The operation of-the voltage compensator shown in Fig. 5 is as follows:

Assuming phase coincidence to have been obtained, the voltage on transformer 18is zero and, "likewise, the direct-current voltage ofrectifier 19 is zero. The battery E, the voltage of which is of a value just suflicient to exactly equal the direct-current voltage of the rectifier 31', when the voltage on line 1-2 is normal, de-energizes the local circuit including the winding 21. That is to say, if

voltages of the line and machine are in phase and the line voltage is at its normal value, equal, of course, to that of the-machine, no current'will flow in the winding 21 and, as explained in connection with Fig. 4, the relay 25 will ass current to energize the operating coil of switch 26, to parallel the machine as above described.

' and the voltage of rectifier 31 will fall in the same proportion. The voltage on transformer 18 will be increased and, likewise,

' that of rectifier 19 by just the same amount that the voltage on transformer 28 decreased. The net result will be that the two circuits will be paralleled, just as if the line voltage had not decreased. It is obvious, of course, that, .without any compensating means, if the line voltage decreased, the resultant of the two circuit voltages would be increased and, by sending current through the winding 21 of the transformer 20, would tend to prevent paralleling. The use of my compensating means, however, makes it possible to automatically parallel the circuits with less exact agreement in phase when the line voltage is decreased. In other words, the system using the compensator will cause paralleling to take place at a wider phase angle, if the voltage of the line is low than if it is normal. This, of course, makes the paralleling operation quicker and places the incoming generator on'the line to boost the line voltage, with a minimum loss of time.

The operation of my voltage compensator may be explained with reference to Fig. 6, in which OL and OM represent line and mafchine voltages. In the positions shown, the resultant of these voltages is LM. Now assume that, for a resultant voltage of LM, the current in the winding 21 of transformer 20 will be sufficiently low to permit energization of the relay 25, paralleling will take place whenever the voltages of the line and machine take such relative positions that the resultant thereof is equal to or less than voltageLM.

Now, if the voltages OL and OM have the positions shown and if the linevoltage OL decreases to the value OL, it is apparent that the resultant of the line and machine voltage will increasefrom the value LM to the value LM. This increase in the resultant voltage tends to prevent energization of the relay 25 and consequent paralleling of the two circuits. With the voltage at the value OL, it would be necessary for the line voltage to take the position OP before the resultant of the line and machine voltages would be reduced sufficiently to permit paralleling. It is obvious, therefore, that, unless some cornpensatmg means is provided, a decrease 1n the line voltage will necessitate closer agree.- ment in phase before the circuits will be paralleled.

The use of the compensating means, as described in Fig. 5, prevents a decrease in line voltage from aflecting conditions in the local circuit including the winding 21 of transformer 20. It may be said, therefore that for a given phase angle between the voltages, the

' influence tending to prevent energization of the relay 25 has the same eflect, measured by the distance between lines OM and NL, regardless of a decrease in the voltage of the line. Since this is the case, paralleling will be accomplished by the system of Fig. 5 whenever the line voltage reaches the position ON, if, as has been previously assumed, it was reduced to the value OL'. from its normal value OL. It may thus be seen that a decrease in the line voltagepermits paralleling to take place in the system shown in Fig. 3at a larger angle, for example, angle NOM, than if the voltage of the line isoat its normal value, in which case, it is necessary that the voltages be within the angle MOL.

In other words, the effect of a decrease in I OL to the value OL on the paralleling relay is .the same as if OM decreased simultaneously, in' the same proportion, to the value OM, since the substantial equality of the voltage of battery E and the sum of the voltages of rectifiers 19 and 31 remains unchan ed. -When the line and machine voltages fliave the efiective values OM and CL as far as the paralleling relay is concerned, the resultant voltage NM which prevents paralleling when it exceeds the value LM, is greater than LM only when an angle greater than NOM exists between the line and machine voltages. Consequently, whenever the angle between the voltages is less than NOM, paralleling is effected.

In Fig. 7 I have shown, graphically, the influence of the various factors afl'ecting the operation of the relay 25. The curve A demonstrates the variation of the voltage on the direct-current windin 21 of the transforiner 20 with variation in the line voltage. It is to be noted that a decrease in line voltage below normal does not aflect the voltage on the direct-current winding 21. r

The curve B shows how the angle of phase difierence affects the voltage on the directcurrent winding 21. sents the voltage of battery E which is constant, regardless of other conditions in the local circuit, and opposed to the rectifier voltages. At normal line voltage and exact synchronism, the voltage impressed on the winding 21 by rectifier 31 will be equal and opposite to t at of'the battery E, so that no current will flow through the winding 21 and, hence, the relay 25 will be energized. As the phase angle between the voltages of the cir-' cuits increases in either direction from zero, the resultant of the voltages increases, and, by means of transformer 18 and rectifier 19, causes an increase in the voltage on the windingi21. Whenever the sum of the ordinates of A and Bis greater than the ordinate of C, winding 21 will be energized, and paralleling prevented.

With an increase in the line voltage above normal, the voltage on the direct-current winding will be increased by means of transformer 28 and rectifier 21. If the line volt- The curve ,C repreage decreases below normal, however, the

voltage on the direct-current winding 21 will ,be unchanged. In this way, the tendency of a decrease in the line voltage to require a closer approximation of phase coincidence before paralleling may be entirely nullified, so that paralleling will take place at a wider angle when the line voltage has decreased.

In Fig. 8 is illustrated a relay system which is similar to that shown in Fig. 5, with the exception that the battery E of the latter is replaced by a transformer 30 connected to the incoming generator, the voltage of which is substantially constant, and a'rectifier 33 which serve, in place of the battery, to provide a source of constant direct-current potential to oppose the voltage of rectifiers 31 and 32 in series. The potentiometer 23 is provided to make possible adjustment of the system so that when the circuits are in synchronism and the line voltage is normal, the voltage across the active portion of potentiometer 23 will be equal to that of rectifier 31. Under these conditions, no current flows in winding 21, and relay 25 is energized to cause paralleling. ()peration of the system shown in Fig. 8 is precisely the same as that of Fig. 5.

In Fig. 9 is shown a system which combines with the phase-advance feature of the system shown in Fig. 1 the voltage compensation fea' ture of Figs. 5 and 8. In the system of Fig.

'9, arrangements are made whereby, if the machine is above s nchronous speed and slowing down, para leling will take place when the voltages of the line and machine are approaching coincidence at a predeten mined rate, but, if the machine is below s nchronous speed and speeding up, paralleling will be positively prevented.

This is accomplished by the addition to the circuit shown in Fig. 8 of a second three-leg transformer with a direct-current winding. As in the previous figures, circuits 1-2 and 34 are connected to analternating-currentsystem andto an alternating-current generator. The line 1-2 is connected to a phase splitter 40 which supplies current to the primary of transformer 41. Transformers 42 and 44 are connectedv across the line and the machine leads, while transformer 43 is so connected as to be subject to the resultant of the line and machine voltages. Rectifiers 46 and 47, energized by transformers 43 and 41, are connected to the direct-current windings 53 and 52, of transformers 51 and 50, the cir' cuits including the rectifiers and the windings,

being in parallel. In series with this group of rectifiers, is a rectifier 45, ener 'zed by transformer 42. Rectifier 48 supplies, from transformer 44, a source of constant directcurrent voltage in opposition to the directcurrent voltages of rectifier 45 and rectifiers 46 and 47. The rectifiers 46 and 47 energize the windings 52 and 5 3 on-the center legs of transformers and 51. The primaries of these transformers are connected, in parallel,

to the machine leads through the impedances' 23'. secondaries 56 and 57 energize the thermal elements of relays 59 and 60. A re turn lead 58 is provided for the current circulating through the direct-current windings 52 and 53. The plate circuit of relay 59 ineludes the operating coil of a switch 65, a source of direct-current voltage 6364 and a regulating resistor 62. The plate circuit of relay is connected to the operating coil of switch 65 by means of conductors 69 and 61. As in the previous modifications of my invention, switch 65 may be the paralleling switch or 'may control a local paralleling circuit.

The operation of the system shown in Fig. 9 may be best explained on conjunction with Fig. 10 in which the various vectors have the same reference letters as in the preceding diagrams. Assuming that the machine is being brought up to synchronous speed, the resultant of the line and machine voltages will be impressed on transformer 43 and rectified by the rectifier. 46 and supplied to the winding Upon the occurrence of synchonism between the machine voltage OM and that of the phase splitter, OL, the current in the windmg 52 will be reduced to zero, as a result of the combined action of rectifiers 45 and 47 in series, opposed by the Volta e of rectifier 48.

When the current in the win ing 52 is reduced below a predetermined minimum, the reactance of the. transformer 52 is so increased that the corresponding increase of the secondary voltage is sufficient to heat the filament of the relay 59 to its operating temperature, as described in connection with Fig. 4; When the filament of relay 59 is sufiiciently heated, current will pass through the relay and thence through the operating coil of switch 65, through the direct-current source 6364 and back to the relay through theresistor 62 causing the contacts 66 to be engaged either to parallel the circuits directly, or to close the circuitof the closing coil of a paralleling switch.

When the voltages 0L and OM, as shown in Fig. 10, becomes synchronized, the current in the winding 53 of the transformer 51 is reduced to zero, as a result of the combined voltage of rectifier 45 ,and rectifier 48. That is to say, when-voltages GI. and OM are coincident, voltage on transformer 43 is substantially zero and, if he line voltage is at its normal value, the voltage of rectifier will be equal and opposite to that of rectifier 48, so that the current through winding 53 becomes zero. Under these conditions, relay is energized, with the result that current flows in the circuit including conductors 69, the direct-current source 6864, resistor 62, relay 59 and conductor 61, the relays 59 and 60 being connected in series and the relay 6O shunting the coil of switch 65. As the result of the establishment of this circuit, the operating coil of switch is short-circuited by the relay 60, and, therefore, prevented from ,being energized.

The sequence of these operations may be better understood from a study of Fig. 10. Assuming that the machine is slow, as it will be when being brought up to synchronous speed, the frequency of the line voltage is higher than that of the machine, and, consequently, vector OL revolves faster than vector OM. In this case, the coincidence of vectors OL and OM precedes that of vectors OL and OM. As explained above, the coincidence of vectors OL and OM causes the energization of relay 60 to prevent the operation of the paralleling switch, whereas .the coincidence of vectors OL and OM causes energization of the relay 59, which, in turn, causes the energization of the paralleling switch 65.

' Thus, it will be seen that, under the conditions described, relay 60 will be energized before relay 59, and, consequently, because of the fact that the operating coil of switch 65 is short circuited by relay 60, paralleling by the subsequent energization of relay 59 will be prevented since the plate current of both relays is extinguished at the same instant, as a result of their beingconnected in series.

If, on the other hand, the speed of the machine is greater than synchronous speed, the vector OM will revolve faster than vector 0L and coincidence of vectors OM and OL will precede coincidenceof vectors OM and OL. Under these circumstances, the relay 59 will be energized before relay 60, since relay 59 is responsive to coincidence of vectors OM and OL, and relay 60 is responsive to coincidence of vectors OM and OL. When relay 59 is energized previous to relay 60, the operating coil of switch 65 is energized, and the paralleling switch 66 is closed. It will thus be apparent that in the system of Fig. 9, if the machine is fast and slowing down, paralleling will be effected whenever the frequencies of the two voltages are within a predeten mined range, and that the operation of the paralleling switch will be initiated when the voltages of the two circuits are at an angle of phase difference equal to L'OL. This angle may be adjusted by the adjustment of phase splitter 40 so that the paralleling switch is finally closed recisely at the moment'vectors OL and M coincide. If the machine speed is low, as above explained, paralleling inductance shown in phase splitter. 40 or the phase splitter 40 instead of being connected to the line, may be connected to the machine, so that voltage OM lags voltage OM, and voltage OL is in phase with voltage OL.

The operation of the voltage compensator described in connection with Figs. 5 and 8 is the same in Fig. 9. As a result, when a decrease in line voltage occurs, paralleling is caused at wider angles of phase difference between the line and machine voltages than when the line voltage is normal.

In Fig. 11 is shown a system which is an improvement over that of Fig. 9. By means of this improvement, I am enabled to obtain paralleling at the precise moment of phase coincidence by initiating the closing of paralleling switch in advance of exact coincidence whether the machine is high or low in speed. The provision for locking out the paralleling switch when the voltages of circuits are in phase is also utilized in the system of Fig. 11.

I accomplish these results by adding to the circuits shown in Fig. 9 a second phase splitter 80 which supplies voltage to transformer 81 which, in turn, energizes a rectifier 82. The phase splitter 80 is connected. to the machine leads in contrast to the phase splitter 40 which is connected to the line. The output of rectifier 82 is supplied to the direct-current winding 85 of a third three-leg transformer 83 which has its primary 84 connected to the machine leads through the impedance 23. The secondary 86 of the transformer 83 energizes the filament of a third relay 87. The filaments and plates of relays 59 and 87 are connected in parallel by the conductors 89 and 88, respectively. I

As described in connection with Fig. 9, synchronism of voltages OL and OM (see Fig. 12) causes the current in the winding 53 of transformer 51 to be reduced to zero, the voltageOL and OM being impressed on the transformers 42 and 44, respectively, and the voltages of rectifiers 45 and 48 being opposed. Similarly, coincidence of voltage OL, which is impressed on transformer 41, and voltage OM, which is impressed on transformer 44, will cause the current in transformer winding 52 to be reduced to zero, resulting in the energization of relay 59. In the same manner, coincidence of voltages OL and OM will cause the current in winding 85 of transformer 83 to be 'reducecl to zero, resulting in the energization of relay 87 and the closing of switch 65 to parallel the circuits.

the operation of the paralleling switch 65,-

just as vector OL'coincides With vector OM. Assuming, on the other hand, that the machine speed is high, vector OM will overtake vector 0L and, therefore. vector OM will 00- incide with vector OL before vector OM reaches the position OL. This also will cause the operation of the paralleling switch which is completely closed as exact coincidence between the line and machine voltage is obtained. As in the preceding figure, coincidence' of vectors 0L and OM energizes relay 60 to short circuit the operating coil of the switch 65, but, bythe arrangement. shown in Fig. 11, the relay 59 or the relay 87 will always be energized before the relay 60, and the operation of the paralleling switch will be started when the voltages of the two circuits are at a predetermined angle and are approaching synchronism at a predetermined rate. The operation of the voltage compensator is the same as in the preceding circuits.

It is to be noted, in connection with Fig. 11, that the direct-current windings 52 and 8 5 may be placed on the same transformer, thereby eliminating the thermal relay 87 and the transformer 83, in which case, the relay 59 will always be energized before the relay 60,

whatever the relations of the frequencies of the two circuits.

By employing the thermal relays 59, 60 and 87, the thermal lag characteristic of the filaments is utilized to check the speed of the incoming machine and the duration of the coildition upon which paralleling is to be based. If the speed of the machine is such that paralleling will introduce unstable conditions, the filaments will not be subjected to their heating currents long enough to render the relays conductiy e to effect paralleling. 7

By so integrating the heating eifect of the control currents of the control transformersf proper operating conditions are predetersource of constant direct-current potential,

such as a battery, to oppose the sum of the rectifier voltages.

I claim as my invention? 1. In asystem for automatically paral-. leling alternating-current circuits, a paralleling switch having a finite time of operation, a relay for controlling the operationof said switch, means for energizing said relay to cause the operation of said switch to be initiated at a time before the coincidence of the voltages of said circuits, dependent on the time required for the operation of said switch, said means comprising a transformer having one winding energized. from .one of said circuits, a second winding energized from a phase splitter in the other circuit, and a third winding connected to said relay for energizing the same, the second winding being supplied with direct current by a rectifier connected to said phase splitter, for controlling the energization of said relay.

2. In a system for automatically paralleling alternating current circuits, a paralleling switch having a definite time of operation, a relay for'preventing the operation of said switch and means for energizing said relay. when the voltages of said sources are in phase, so as to prevent the closing of said switch when the circuit voltages are departing from phase coincidence.

3. In a system for automatically paralleling alternating-current circuits, a magneticallyoperated switch having a finite time of operation, for connecting said circuits, and means responsive to synchronism of said circuits to short-circuit the closing coil of said switch to prevent its energization when said circuits are in phase, and commencing to diverge. I

4. In a system for automatically paralleling alternating-current circuits. a magnetically operated switch having a finite time of operation for connecting said circuits and means responsive to phase coincidence of the voltages of said circuits to short-circuit the closing coil of said switch to prevent its ener- 4 gizationwhen said circuits are in phase and means to energize the closing coil when the voltages of said circuits are out of phase by a predetermined angle and approaching coincidence at a predetermined rate, whereby said switch is finally closed precisely at the instant of exact phase coincidence.

5. In a device for automatically paralleling alternating-current sources, a switch for connecting said sources, having a definite time of operation, means for causing the operation of said switch to be inltiated before the voltages of said circuits are exactly in phase circuits and a voltage out of phase with that of the other circuit.

6. In combination with a relay for controlling a switch having a definite time of operation, for paralleling alternating-current circuits, said relay being responsive to phase coincidence of applied voltages, a phase splitter connected in one of said circuits, and means for applying to said relay the voltage of the other circuit and a voltage in phase with the current in said phase splitter, whereby the closing of said switch will be initiated in advance of exact coincidence of the voltage of said circuits by a time interval corresponding to that required for the operation of said switch.

' 7 In a system for automatically paralleling an alternating-current generator with an alternating-current line, a paralleling switch, a relay for controlling said switch, means for energizing said relay from said generator, and means tending to increase the energization of said relay when the voltages of the generator and line are in phase and compensating means for maintaining the energization of said relay when the voltage of said line decreases, whereby paralleling of said generator and line is accomplished more readily if the voltage of said line is low than if it is normal or higher than normal.

8. A system for automatically connecting alternating-current circuits comprising a connecting switch controlled by a relay, a phase splitter connected in one of said circuits, rectifiers connected to said circuits and to said phase splitter, a three-leg transformer having a direct-current winding on the central leg, in series with said rectifiers, windings on the other legs of said transformer connected respectively to one of said circuits and to said relay, whereby the relay is-ener gized in accordance with the current inthe direct-current winding.

9. In a system for automatically connecting alternating-current circuits, a connecting switch, a relay for controlling said switch, a transformer connected to one circuit for energizing said relay, a direct-current winding on said transformer for reducing the energization of said relay and means for causing direct-current to circulate in said direct-current winding, andcompensating means connected to one of said circuits for opposing the flow of direct-current in said winding.

10. In a system for automatically connecting alternating-current circuits, a connecting switch, a relay for controlling said switch, a transformer connected to one of said circuits and having a direct-current winding which when energized reduces the voltage of the transformer, a relay energized by said transformer, and means for circulating direct-current through said direct-current winding in proportion to the resultant of the voltages of said circuits, and compensating means for preventing an increased flow of direct current when the voltage of one of said sources decreases.

11. In a system for automatically connecting alternating-current circuits, a connecting switch, and a relay for controlling the operation of said switch, a transformer having windings connected to one of said circuits and to said relay respectively, rectifiers connected to said circuits and a third winding supplied with direct current from said rectifiers 12. In a system ing alternating-current circuits, including a connecting switch and a relay for controlling its operation, means for compensating for a decrease in the voltage of one of said circuits, comprising means for reducing the energization of said relay in proportion tothe resultant of the voltages of said circuits and means for opposing said reduction in proportion to the decrease in the voltage of one of them.

In testimony whereof, I have hereunto sub-- scribed my namethis 27th day of September,

PHILLIPS THOMAS.

for automatically connect- I 

